- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄359439 > VT900 (PerkinElmer Inc.) Photoconductive Cells and Analog Optoisolators (Vactrols) PDF資料下載
參數(shù)資料
| 型號(hào)： | VT900 |
| 廠商： | PerkinElmer Inc. |
| 英文描述： | Photoconductive Cells and Analog Optoisolators (Vactrols) |
| 中文描述： | 光導(dǎo)細(xì)胞和模擬光隔離器（Vactrols） |
| 文件頁數(shù)： | 62/76頁 |
| 文件大?。?/td> | 1240K |
| 代理商： | VT900 |
第1頁第2頁第3頁第4頁第5頁第6頁第7頁第8頁第9頁第10頁第11頁第12頁第13頁第14頁第15頁第16頁第17頁第18頁第19頁第20頁第21頁第22頁第23頁第24頁第25頁第26頁第27頁第28頁第29頁第30頁第31頁第32頁第33頁第34頁第35頁第36頁第37頁第38頁第39頁第40頁第41頁第42頁第43頁第44頁第45頁第46頁第47頁第48頁第49頁第50頁第51頁第52頁第53頁第54頁第55頁第56頁第57頁第58頁第59頁第60頁第61頁當(dāng)前第62頁第63頁第64頁第65頁第66頁第67頁第68頁第69頁第70頁第71頁第72頁第73頁第74頁第75頁第76頁
57
Application Notes—Analog Optical Isolators
APPLICATION NOTE #1 AudioApplications
The LDR output element of AOIs is almost purely resistive in nature.
This property makes the AOI a very useful device for the control of AC
signals. Further because AOIs also possess very low noise and low
harmonic distortion characteristics, they are ideal for use as variable
resistors, capable of being remotely adjusted in a wide range of audio
applications and control circuits.
The focus of this note is on the use of AOIs in audio applications.
However, many of the approaches used are equally applicable to
higher frequency AC amplification and control circuits.
Control Circuits
Voltage Divider Circuits
The output element of the AOI is a two termnal variable resistor and
may be used in a voltage divider circuit as shown in Figures 1a and 1b.
Shunt Input Control
Figure 1a shows the AOI as the shunt element. With I
F
= 0, the
photocell has a very high resistance so e
out
= e
in
. When I
F
is injected
into the LED, the AOI output resistance decreases pulling down the
output voltage. Since the cell cannot be driven to zero resistance, the
value of R
1
must be selected to give the desired maximumattenuation.
A VTL5C4 with a maximum“on” resistance of 200 ohms at I
F
= 10 mA
requires an R
1
of 6100 ohms for 30 db voltage attenuation (producing
a 1000:1 power ratio). The actual attenuation ratio will be greater since
the 10 mA “on” resistance is typically 125 ohms.
When the maximumI
F
is less than 10 mA, the series resistance must
be greater to get the same attenuation ratio. If R
1
is made large, the
insertion loss (db attenuation at I
F
= 0) will be higher when the output is
loaded. The maximumvoltage across the photocell in this circuit is
equal to the input voltage assumng no insertion loss. An input voltage
as high as 5 – 10V will produce noticeable distortion but that will drop
as I
F
is increased. To mnimze distortion, the voltage across the cell
should be kept below 1.0V at the normal operating point.
Series Input Control
With an AOI as the series element as shown in Figure 1b, e
out
=0 at I
F
= 0. The maximumvoltage across the cell is e
in
, but decreases as I
F
increases.
Op-Amp Feedback Resistor Control
The AOI may also be used as the input or feedback resistor of an
operational amplifier. When used in the feedback loop, Figure 1c, a
fixed resistor should be used in parallel. With no parallel limting
resistor, the feedback may approach an open circuit condition at
maximumgain. In this open loop state, the circuit becomes unstable
and may latch up. The parallel resistor R
3
sets the maximumgain of
the amplifier and stabilizes the DC output voltage. Resistor R
2
is in
series with the AOI output and sets the mnimumgain of the circuit. For
op-amps with unity gain compensation, R
2
is set equal to R
3
so the
circuit gain does not drop below one. The maximumvoltage on the cell
(LDR) is e
out
. If mnimzing distortion is a consideration, e
out
should be
kept below 1.0V.
Op-Amp Input Resistor Control
When the AOI is used as the input resistor of an op-amp, Figure 1d, a
fixed resistor in series will limt the maximumgain as well as prevent
overload of the previous stage.
Non-Inverting Op-Amp Circuits
The AOI can also be used in non-inverting op-amp circuits. Gain is
controlled potentiometrically and, again, resistors should be used to
limt the maximumgain. The circuit of Figure 1e requires a resistor in
series with the AOI, while the circuit of Figure 1f requires one in
parallel.
General Considerations
The circuit application and AOI characteristics will influence the choice
of circuit to use. In Figure 1a to 1f, gain vs. I
F
curves are given for each
circuit, as well as input impedance and gain formulas. Once the proper
circuit function is selected, AOI response speed must be considered.
Because an LDR (photocell) turns “on” fast and “off” slowly, circuits of
Figure 1d and 1e will increase in gain rapidly but be slower in the
decreasing gain. The circuits of Figure 1c and 1f respond faster when
the gain is reduced. All other design considerations are the same as
they would be for any op-amp circuit. In all the amplifier configurations,
a gain ratio of 1000:1 or higher can be achieved.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| VT905GA | |
| VT905GC | |
| VT90N1 | |
| VT90N2 | |
| VT90N3 | |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| VT905GA | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| VT905GB | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| VT905GC | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| VT90A114 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| VT90A432 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。